Electrophotographic materials

ABSTRACT

A photosensitive material for electrophotography comprising an organic photoconductive compound and a sensitizer consisting of reaction products of a benzopyrylium salt and a benzopyrane.

United States Patent Inventors Yoshinobu Murakami;

Kazuhisa Morimoto, both of Osaka, Japan Appl. No. 4,200 Filed Jan. 20, 1970 Patented Nov. 2, 1971 Assignee Matsushita Electric Industrial Co., Ltd.

Kadoma, Osaka, Japan Priority Jan. 30, 1969 Japan 44/ 7501 ELECTROPHOTOGRAPHIC MATERIALS 7 Claims, 6 Drawing Figs.

U.S. CI 96/l.5,

[5 1] Int. Cl 603g 5/06 [50] Field of Search 96/15, 1.6; 252/501 [56] References Cited UNITED STATES PATENTS 3,250,615 5/1966 Van Allan et al. 96/L6X 3,526,502 9/1970 Murakami et al 96/].5

Primary Examiner-Charles E. Van Horn Attorney-Wenderoth, Lind & Ponack ABSTRACT: A photosensitive material for electrophotography comprising an organic photoconductive compound and a sensitizer consisting of reaction products of a benzopyrylium salt and a benzopyrane.

PATENIED mwz I97l 3.617.268

Wave Length (m u) FIG, 5

i Sample No.39

/ful Wave Length ("m u) Sample Non28 700 600 500 400 NVWfO/P Wave Le g (hr u) YUSHINOBU MURAKAMI ELECT ROPHOTOGRAPHIC MATERIALS This invention relates to an electrophotographic material and more particularly to a photoconductive insulating material comprising an organic photoconductive compound and a sensitizer.

Various photoconductive insulating layers are well known in the electrophotographic art for making copies of documents, drawings, transparencies, etc. These layers contain on organic photoconductive compound, such as poly-N-vinylcarbazole, poly-3,6-dibromo-N-vinylcarbazole, brominated poly- N-vinylcarbazole, nitrated poly-N-vinylcarbazole, polyacenaphthylene, etc. These layers are nonconductors of electricity before exposure and become electrical conductors upon exposure.

It is necessary for the electrophotographic art that the photoconductive insulating material has a high photoconductivity in the region of the visible spectrum. Such a photoconductive insulating material makes it possible for the electrophotographic art to employ inexpensive and convenient light sources such as incandescent lamps in a reduced exposure time and to reproduce colored pictures. The photoconductive compounds mentioned above, however, have usually a low photoconductivity and spectrum characteristics sensitive to the short wavelength region of the exposure light and do not satisfy entirely the above requirement.

It is known that an addition of a so-called sensitizer can improve photoconductivity and spectrum response of the above photoconductive compounds. Conventional sensitizers are dyestuffs, such as triarylmethane dyes, xanthene dyes, triazine dyes or acridine dyes, but the conventional sensitizers are-not entirely satisfactory for improvement of the photoconductivity and the spectrum response of the available organic photoconductive compounds.

In addition to the high photoconductivity and spectrum response sensitive to visible light, the electrophotographic art requires a high electric resistance of photoconductive materials in the dark. Conventional sensitizers promote the photoconductivity but increase the dark conductivity. A high dark conductivity of photoconductive materials is not desirable because it results in a loss of the applied electrostatic charge in the dark.

OBJECT OF THE INVENTION response sensitive to visible light.

Another object of the invention is to provide electrophotographic materials having a high electric resistance in the dark.

EXPLANATION OF FIGURES These and other objects of the present invention will be apparent upon consideration of the following detailed description taken together with accompanying drawings wherein:

FIG. 1 represents the absorption spectra, in 1,2- dichloroethane, of one example (Sample Number 27) of sensitizers according to the present invention under comparison with those of 2-(p-methoxystyryl)-3-phenylbenzopyrylium perchlorate (Compound Number 2), in 1,2-dichloroethane, and Z-(p-methoxystyryl)-3-phenyl-4-methoxypyrane (Compound Number ll) in methanol.

FIG. 2 represents the infrared absorption spectra in KBr method ofCompound Number 2, 11 and Sample Number 27.

FIG. 3 represents the wedge spectrogram for an electrophotographic material coated with a solution containing weight percent of brominated poly-n-vinylcarbazole and 0.02 weight percent of sensitizer (Sample Number 27), the brominated poIy-N-vinylcarbazole being dissolved in a solvent consisting of4 parts by weight of chlorobenzene and 1 part by weight of 1,2-dichloroethane under comparison with those of brominated poly-N-vinylcarbazole.

FIG. 4 represents the wedge spectrogram of an electrophotographic material coated with a 10 weight percent solution of brominated poly-N-Vinylcarbazole sensitized with 0.02 weight of Sample Number 50, the brominated poly-N- vinylcarbazole being dissolved in a solvent consisting of 4 parts by weight of chlorobenzene and 1 part by weight of 1,2- dichloroethane, under comparison with the wedge spectrogram of an electrophotographic material coated with a 10 weight percent solution of brominated poly-N-vinylcarbazole sensitized with 0.06 weight percent of Compound Number 9, which is the raw material of Sample Number 50, the brominated poly-N-vinylcarbazole being dissolved in a solvent consisting of 4 parts by weight of chlorobenzene and 1 part by weight of 1,2-dichloroethane.

FIG. 5 represents the wedge spectrogram of an electrophotographic material coated with a 10 weight percent solution of poly-N-vinylcarbazole sensitized with 0.03 weight percent of Sample Number 39, the poly-N-vinylcarbazole being dissolvedin a solvent consisting of 4 parts by weight of toluene and 1 part by weight of l,2-dichloroethane.

FIG. 6 represents the wedge spectrogram of an electrophotographic material coated with l0 weight percent solution of poly-N-vinylcarbazole sensitized with 0.03 weight percent of Sample Number 28, the poly-N-vinylcarbazole being dissolved in a solvent consisting of 4 parts by weight of toluene and 1 part by weight of l,2-dichloroethane.

SCOPE OF INVENTION wherein R is an aliphatic group such as styryl, p-methoxystyryl, w-phenylbutadienyl; aromatic group such as phenyl, pmethoxyphenyl;

R is selected from the group consisting of hydrogen and phenyl radical;

R is selected from the group consisting of hydrogen and methoxy radical;

Anion is fluoborate chloroferrate, perchlorate anion. The chemical formula B is chlorozincate or /O -RI l L...

wherein R is an aliphatic group such as styryl, p-methoxystyryl,

w-phenylbutad'ienyl; aromatic group such as phenyl, pmethoxyphenyl;

R, is selected from the group consisting of hydrogen and phenyl radical;

R is selected from the group consisting of hydrogen and methoxy radical.

Said reaction products can be formed by employing the following steps which comprise (1) providing a solution of said benzopyrylium salt in a suitable solvent such as 1,2- dichloroethane, (2) providing a solution of said benzopyrane in a suitable solvent such as l,2-dichloroethane, (3) mixing both solutions and heating the mixed solution (4) pouring the heated solution into a suitable precipitant such as ether to form a precipitate separating the precipitate from the precipitant and (6) purifying the separated precipitate.

BENZOPYRYLIUM SALT There have been known four methods for preparing the benzopyrylium salt. The first method is a modification of a method disclosed in J. Chem. Soc.. i935, page 941 and is based on the reaction of a phenol or phenol derivative with a B-dicarbonyl compound or an a,B-unsaturated ketone in the presence of hydrogen chloride, sulfuric acid, ferric chloride, acetic or formic acid.

The second method comprises using an intermediate product prepared from a phenol and a coumarin derivative in the presence of phosphorus oxychloride or zinc chloride in a similar way to that disclosed in Helv. chim. acta, 34, page 1761 (1951).

The third method is based on a method disclosed in J. Chem. Soc., 74, page 3,445 (1952). A ring closure process of an o-hydroxybenzaldehyde and a carbonyl compound in the presence of an alkali forms a benzopyrylium ring. An ethenyl group of an active a-methylene radical in the 2-position of 2- alkylbenzopyrylium has an important role on the benzopyrylium ring closure process.

The fourth method is based on a method disclosed in J. Chem. Soc., 1929, page 936 and is effected in one step by both ring closure and ethenylation of an o-hydroxybenzaldehyde with a carbonyl compound in the presence of an alkali.

Examples of suitable benzopyrylium salt are given in table 1 below.

TABLE 1 Absorption maximum ing! l) Compound in 1,2411- Number Name of compound chloroethano 1 2-(a-isopropyl-w-phenylbutadienyl)-benzo- 530 pyrylium perchlorate. 2 Z-(p-methoxystyryl)-3-phenylbenzopyryli- 552 um perchlorate. 2B 2-(p-methoxystyryl)-3-phenylbenzopyryli- 560 um fiuoborate. 2F 2-(p-methoxystyryl)-3-phenylbenzopyryli- 560 um chloroferrate. 22 Z-(p-methoxystyryl)-3-phenylbenzopyry1i- 560 um chlorozineate. 3 2-(p-methoxystyryl)-3-pheny1-8-methoxy- 555 benzopyrylium perchlorate. 4 2-(p-methoxyphenyl)-benzopyrylium per- 455 chlorate. 5 2-(pmethoxyphenyl)-8-methoxybenzopyryl- 460 ium perchlorate. 6 2-st3g'yl-3-phenylbenzopyrylium perchlo- 503 ra e. 7 2-(a-isopropyl-p-methoxystyryl)-benzopy- 543 rylium perchlorate. 8 Z-(a-isopropylstyryl)benzopyrylium per- 458 chlorate. 9 Z-phenylbenzopyrylium perchlorate 410 Exam pTes of reaction prTeim'e to prepare z fb eniopywli um salt are shown as follows:

l. 2-(p-Methoxystyryl)-3-phenylbenzopyrylium perchlorate (Compound Number 2) 5 grams ofsalicylaldehyde and 5.5 grams of phenylacetone are dissolved in milliliters of formic acid in order to obtain a solution and dry hydrogen chloride gas is slowly blown into the solution in an ice-cooled bath for L5 hour. After standing in an icebox for 3 hours the solution is added 6 grams of panisaldehyde and 25 milliliters of formic acid, then dry hydrogen chloride gas is slowly blown into the solution in an ice-cooled bath for 1 hour. After standing overnight at a room temperature, the solution in an ice-cooled bath has 90 milliliters of 10 percent perchloric acid added slowly thereto while being stirred. Precipitation starts when the perchloric acid is added to the solution. The precipitate obtained is filtered off, washed thoroughly with ether and recrystallized from an acetic acid to yield 7 grams of needle-crystal which has a melting point of229 to 230 C.

2. 2-(a-lsopropylstyryl)-benzopyrylium perchlorate (Compound Number 8) 20 grams of 2-oxystyrylisobutyl ketone and i0 grams of benzaldehyde are dissolved in milliliters of ether in order to obtain a solution and I5 grams of 60 percent perchloric acid is slowly added to the solution. Precipitation starts when the solution is saturated with dry hydrogen chloride gas. The solution and precipitate are then allowed to stand overnight in an icebox, and the resulting precipitate is collected by filtration, washed thoroughly with ether. The crude product obtained is recrystallized from a solvent consisting of 5 parts by weight or acetic acid and 1 part by weight of dichloroethane to yield 10 grams of crystal, having a melting point of 169 to l70 C.

Other benzopyrylium procedures as stated above.

BENZOPYRANE The benzopyranes are easily prepared by one of the following two methods. A first method is that benzopyrane is prepared by heating, under a reflux, a methanol solution of said benzopyrylium salt with sodium bicarbonate. A second method is that benzopyrane is prepared by heating an alcohol solution of said benzopyrylium salt with sodium hydroxide or potassium hydroxide.

Examples of suitable benzopyranes are given in table 2 below.

salts are obtained by similar Examples of reaction procedure to prepare a benzopyrane are shown as follows:

3. 2-(p-Methoxystyryl)-3-phenyl-4-methoxybenzopyrane (Compound Number 11) 4 grams of Z-(p-methoxystyryl)-3-phenylbenzopyrylium perchlorate are dissolved in 800 milliliters of hot methanol in order to obtain a solution. Then, 10 grams of sodium bicarbonate is added to the cold solution. After the solution is refluxed for 10 minutes, the solution is cooled and a precipitate obtained is collected by filtration and washed with methanol. The filtrates are distilled by a rotary evaporator to yield a crude compound. The crude compound filtered off is dissolved in 500 milliliters of methanol under heating in order to obtain a solution, then, the solution is cooled, added 500 milliliters of water and allowed to stand overnight. The resulting precipitate having a melting point of 84 to 86 C. is then collected by filtration.

4. 2-Styryl-3-phenyl-4-methoxybenzopyrane (Compound Number 13) Similarly to the procedure as stated above, 2.5 grams of yellow crystal having a melting point of 63 to 66 C. is obtained from 4 grams of 2-styryl-3-phenylbenzopyrylium perchlorate.

Other benzopyranes are obtained by the similar procedure as stated above.

The benzopyrane thus obtained is unstable and tends to change to a benzopyrylium salt by adding organic acid or inorganic acid. Furthermore, the benzopyrane is colored by air. Therefore, an improved preparation procedure is developed as follows: in the preparation procedure such as procedure (3) or (4), the crude benzopyrane is not recrystallized from a methanol-water solution, but the crude compound is shaken in SENSITIZER The sensitizer according to the present invention is produced by the reaction of a benzopyrylium salt and a benzopyrane. Examples of the reaction products are shown in table 3 with their physical properties.

TABLE 3 mer. l- M.P. in'1,2-d1- C.) chloroethane Compounds:

N and No 167-171 540, 670 10 and N o. 138-141 580, 620 10 and No. 154-157 465, 670 10 and No. 158-162 455, 676. 10 and No. 156-159 570, 680' 10 and N0. 167-171 685 10 and No. 163-167 685 10 and No. 181-184 545, 675 11 and No. 183-185 595, 625 11 and No. 162-165 595, 645 11 and No. 150-154 595, 645 11 and N0. 115-119 595, 645 11 and No. 176-179 595, 645 11 and No. 206-209 555, 595 11 and. No. 168-171 550, 590 11 and No. 157-160 595, 700 11 and N0. 138-140 500, 590 11 and No. 136-138 585, 650 11 and N0. 157-161 545, 635 12 and No. 224-225 590, 640 13 and N0. 159-163 630, 700 13 and No. 163-166 590, 640, 700 13 and N0. 156-160 550, 593, 710 13 and No. 163-167 550, 590, 705 13 and No. 170-174 595, 640, 705 13 and No. 145-148 595, 705 13 and N0. 139-142 588, 705 13 and No. 218-220 585, 705 14 and No. 126-129 610, 690 14 and N 0. 122-125 540, 580 14 and No. 118-121 610 14 and No. 25-129 610 14 and No. 136-14O 540, 580 14 and No. 124-127 505, 610 14 and No. 113-116 610 14 and N0. 144-147 610 15 and No. 151-154 550, 590 15 and No. 145-150 630 15 and No. 131-135 530, 590 15 and No. 14%145 630 16 and No. 156-160 560, 580 16 and No. 151-155 565, 685 16 and No. 116-119 690 16 and N0. 124-127 515 17 and No 2 11%116 550, 585 17 and No 6 128-131 585. 680 17 and N0. 8 83-87 555, 690 17 and No. 9 118-122 590 The formation of sensitizer according to the present invention is accomplished by heating a solution of the benzopyrylium salt and benzopyrane in a suitable solvent such as dichloroethane at 40 to 70 C. for several hours to dozens of hours. The amount of benzopyrane to be used is oneto three times by molar weight of benzopyrylium salt to be used. The color of the solution changes to dark color with a progress of the reaction. For example, FIG. 1 shows the absorption spectra of, Compound Number 2 (in dichloroethane) and Compound Number 11 (in methanol), and reaction product, Sample Number 27 (in dichloroethane). When Compound Number 2 (reddish violet) reacts with Compound Number 11 (pale yellow), the color of the reacting solution changes from reddish violet to blue. After the completion of the reaction, the solution is poured into ether to obtain a crude product. The crude product is dissolved in dichloroethane, then, the solution is poured into ether to yield a pure reaction product. As shown in H6. 2 at the spectrum of Sample Number 27, the

infrared absorption bands 1,478, 1,375 and 975 cm are distinguished as compared with Compound Number 2.

Some examples of methods of preparing the sensitizer are set forth below in accordance with table 3. It will be apparent to those skilled in the art that other sensitizers according to the present invention may be prepared by methods similar to those described in general hereinabove and specifically herein below.

I. Sample Number 26 3.6 grams of Compound Number 11 and 2.0 grams of Compound Number 1 are dissolved in 40 milliliters of 1,2- dichloroethane which is purified to eliminate an acidic material by sodium carbonate. A so-obtained solution is stirred at 50 C. for 5 hours. The color of the solution is red at the beginning of the reaction, but, the color changes in accordance with the reaction progress. At the end point of the reaction the color of the solution is blue. After the completion of the reaction, the solution is cooled :to 24 C. and poured into 300 milliliters of ether to yield a precipitate. The precipitate is washed thoroughly with ether, dried and dissolved indichloroethane to obtain a solution. The solution is poured into-ether to yield 2.5 grams ofcrystal having a melting point of l83"to 185C.

ll. Sample Number 39 3.4 grams of Compound Number 13 and 2 grams of Compound Number 6 are dissolved in 75 milliliters of 1,2- dichloroethane which is purified to eliminate an acidic material. A so-obtained solution is stirred at 50 C. for 8 hours. After the same procedure as stated in (l), 3 grams of crystal is the yield. The crystal has a melting point of l70 to 174 C. and a solution of the crystal in 1,2-dichloroethane is green.

lll. Sample Number 50 4.8 grams ofCompound Number 14 and 3 grams of Compound Number 9 are dissolved in milliliters of pure 1,2-

dichloroethane to obtain a solution. The solution is stirred at- 50C. for 8 hours. The same procedure as stated in (l) yields 5 grams of crystal. The crystal has a melting point of 144 to 147 C. and a solution of the crystal in l,2-dichloroethane ispound Numb'er'4' are dissolved in 40 milliliters of pure 1,2- dichloroethane to obtain a'solution. The solution is stirred at 50 C. for 20 hours, during which the color of the solution changes from-orange to green. After the same procedure as stated in (l), 3 grams of crystal is the yield. The crystal has a melting po'intof l45 to 150 C.

PHOTOCONDUCTIVE lNSULATlNG MATERIAL An improved photoconductive insulating material adapted for aforesaid photoconductive insulating layer can be obtained by a combination of aforesaid sensitizer and aforesaid organic photoconductive compound selected from the group consisting of poly-N-vinylcarbazole, poly-3,6-dibromo-N- vinylcarb'azole, brominated poly-N-vinylcarbazole, nitrated poly-N-vinylcarbazole and polyacenaphthylene. The sensitizer according to the present invention is usually added to a solution of the'phot'oconductive compound in the form of a solution in a suitable solvent, such as dichloroethane, methylene chloride, chloroform, or a combination thereof. An added amount of said sensitizer is from 0.005 gram to 0.02 gram, preferably from 0.00l5 gram to 0.015 gram with respect to 1 gram ofsaid organic photoconductive compound.

Poly-3,6=dibromo-N-vinylcarbazole and brominated poly- Nvinylcarbazole'are prepared by the methods described in U.S. Pat. No: 3,421 .891. Nitrated poly-N-vinylcarbazole is prepared by the method described in U.S. Pat. No. 3,418,116. Other polymers are prepared by well-known methods.

F6 the preparation of the photoconductiveinsulating layers, a solution of the photoconductive polymer and the sensitizer in a suitable solvent is applied to the supports in the usual manner, for example, spraying, blade coating, wire-rod" coating or whirler coating, and then dried so as to produce a homogeneous photoconductive insulating layer on the electroconductive support. Suitable solvents are benzene, toluene, chlorobenzene, dioxane, methylene chloride, dichloroethane and combinations thereof. The solution may include suitable plasticizers and/or organic colloids for improving the flexibility and strength of the photoconductive compound layer. Suitable plasticizers include chlorinated diphenyl, dimethyl phthalate, diethyl phthalate and octyl phthalate. Suitable organic colloids include natural and synthetic resins, e.g. phenol resin, phenol resin modified wit h rosin polyvinyl acetal, polyvinyl butyral, polyvinyl cinnamate and polycarbonate resin. Suitable materials for a conductive support layer are those materials which satisfy the requirement of the electrophotographic art and include metal plates, glass plates having NESA coating and plates or foils made of electrically conductive resins or coated with a vacuum-deposited thin metal layer. Transparent supports can be used to form transparent .electrophotographic plates, foils or films.

The reproduction of images by electrophotographic ,methods is carried out as follows: when the photoconductive insulating layer has been charged by means of a corona discharge apparatus, the electrophotographic material with the photoconductive insulating layer is exposed to light under a master and is then dusted over in a known manner with a resin powder colored with carbon black. The image that now becomes visible can easily be wiped off. It can also be fixed by heating at about 120 C. From positive masters, positive images exhibiting good contrast are produced.

EXAMPLE This invention is still further illustrated with reference to the following examples which are given by way of illustration only.

EXAMPLE 1 One gram of poly-N-vinylcarbazole, 0.004 gram of a sensitizer listed in table 3 and 0.5 gram of chlorinated diphenyl (commercially available as Kanechlor") are dissolved in 10 milliliters of l,2-dichloroethane. The solution is applied to an aluminum plate and is dried to form a layer [p in thickness. After the aluminum plate provided with the layer is charged positively by means of corona discharge with a charging device maintained at approximately 6,000 volts in the dark, it is placed under a positive master and is exposed to a l00 W tungsten lamp at an illumination of 50 luxes. Subsequently, the plate is powdered over with a developer in a per se known manner. This developed consists of a toner and a carrier. The toner consists of a low melting-point polystyrene, colophony and carbon-black and is mixed with a carrier substance having a nature such that the toner becomes triboelectrically charged with a charge opposite to that produced on the plate. A positive image is produced and is fixed by slight heating. Table 4 shows the optimum amounts of exposure in lux-second units.

It is clear from table 4 and FIGS. 5 and 6 that the sensitizers improve the photoconductivity and the spectrum response of poly-N-vinylcarbazole.

TABLE 4 Compound No. Optimum Exposure (lux.sec.)

EXAMPLE 2 One gram of polyacenaphthylene. 0.6 gram of chlorinated diphenyl (commercially available as Kanechlor) and 0.004 gram of a sensitizer listed in table 3 are dissolved in 10 milliliters of l,2-dichloroethane The solution is applied to an aluminum plate and is dried to form a layer 6;; in thickness. An

electrophotographic image is produced in the same way as that described in example 1. Table 5 shows the optimum amounts of exposure in lux-second units to produce exactly the original images.

TABLE 5 Compound No. Optimum Exposure (lux.see.)

None 200,000 27 $1 30 60 34 79 39 56 EXAMPLE 3 Two grams of nitrated poly-N-vinylcarbazole (containing nine nitrated carbazole rings per a hundred carbazole rings), 1 gram of chlorinated diphenyl (commercially available as Kanechlor") and 0.004 gram of a sensitizer listed in table 3 are dissolved in 10 milliliters of l,2-dichloroethane. The solution is applied to an aluminum plate and is dried to form a layer l2 in thickness. An electrophotographic image is produced in the same way as that described in example 1. Table 6 shows the optimum amounts of exposure in luxsecond units to produce exactly the original images.

EXAMPLE 6 Compound No. Optimum Exposure (lux.sec)

(monobromo-substituted product), 5 grams of polycarbonate resin (commercially available as Panlite K), 3 grams of chlorinated diphenyl (commercially available as Kanechlor and 004 gram of a sensitizer listed in table 3 are dissolved in a solvent containing 80 milliliters of chlorobenzene and 20 milliliters of 1,2-dichloroethane. This solution is applied to an aluminum plate and is dried to form a layer 14p. thickness. An electrophotographic image is produced in the same way as that described in example 1. Table 7 shows the optimum amounts of exposure in lux-second units to produce exactly the original images.

It is clear from table 7 and FIGS. 3 and 4, that the sensitizers improve the photoconductivity and the spectrum response of brominated poly-N-vinylcarbazole.

TABLE 7 Compound No. Optimum Exposure (lux.sec)

None 80,000 18 56 I9 26 20 80 22 30 23 52 24 56 26 15 27 15 17B 10 27F 13 272 I4 28 I8 29 20 30 15 3! i6 32 I5 33 I7 34 20 35 i5 36 I5 37 I7 38 20 39 i6 40 19 41 20 42 I8 43 85 44 25 45 58 46 7 47 44 4s 70 50 40 51 24 52 4o 53 40 54 36 55 36 s 40 57 so 58 65 59 25 60 32 61 75 62 90 EXAMPLE 5 One gram of poly-3,6-dibromo-N-vinylcarbazole, 0.4 gram of chlorinated diphenyl (commercially available as Kanechlor") and 0.004 gram of a sensitizer listed in table 3 are dissolved in milliliters of 1,2-dichloroethane. Thesolution is applied to an aluminum plate and is dried to form a layer 8 1 in thickness. An electrophotographic image is produced in the same way as that described in example 1. Table 8 shows the optimumv amounts of exposure in luxsecond units to produce exactly theoriginal images.

TABLES Compound No. Optimum Exposure (luxsec) None 5,000 19 2| 20 22 24 23 26 9 27 9 28 I0 Applicants preferred sensitizing compounds are those selected from the reaction products of a benzopyrylium salt having the chemical formula T Anionwherein R is a'radical selected from thejgroup consisting of a- -isopropyl-w-phenylbutadienyl, methoxystyryl, methoxyphenyl, styryl, a-isopropyl methoxystyryl a-isopropylstyryl and .phenyl,

R is hydrogen or phenyl,

R is hydrogen or methoxy,

and the anion is selected from the group consisting of fluoborate, chloroferrate, chlorozincate and perchlorate wherein R is aradical selected from the group consisting of styryl, methoxystyrl, a-isopropyl-m-phenylbutadienyl. aisopropyl-methoxystyryl, phenyl, a-isopropyl styryl and methoxyphenyl,

R is hydrogen or phenyl, and

R is hydrogen or methoxy.

What is claimed is:

1. An electrophotographic material comprising a conductive support layer and a 'photoconductive in'sulating'layer, the latter comprising a combination of an organic photoconductive compound :and a sensitizer, said organic photoconductive compound consisting essentially of at least one compound selected from the group consisting of poly-N-vinylcarbazole, poly-3,6-dibromo-N-vinylcarbazole, brominated poly-N-vinylcarbazole, nitrated poly-N-vinylcarbazole and polyacenaphthylene, said sensitizer comprising a compound selected from the group consisting of reaction products of a l)enzopyryliunisalt ha ving the chemical formula I I Anionwherein R is a radical selected from the group consisting of aisopropyl-wphenylbutadienyl, methoxystyryl, methoxyphenyl, styryl, a-isopropyl methoxystyryl, a-isopropylstyryl and,

wherein R, is a radical selected from the group consisting of styryl. methoxystryl a-isopropyl-w-phenylbutadienyl. aisopropyl-methoxystyryl, phenyl, a-isopropyl styryl and methoxyphenyl,

R is hydrogen or phenyl, and

R is hydrogen or methoxy.

2. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of Z-(a-isopropyl-w-phenylbutadienyl)-benzopyrylium perchlorate and Z-(p-methoxystyryl)-3-phenyl-4-methoxypyranev 3. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2- p-methoxystyryl)-3 phenyl-benzopyrylium perchlorate and -(p-methoxystyryl)- 3-phenyl-4-methoxypyrane.

4 The electrophotographic material of claim 1 wherein the 

2. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2-( Alpha -isopropyl- omega -phenylbutadienyl)-benzopyrylium perchlorate and 2-(p-methoxystyryl)-3-phenyl-4-methoxypyrane.
 3. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2-(p-methoxystyryl)-3-phenyl-benzopyrylium perchlorate and 2-(p-methoxystyryl)-3-phenyl-4-methoxypyrane.
 4. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2-(p-methoxylphenyl) benzopyrylium perchlorate and 2-(p-methoxystyryl)-3-phenyl -4-methoxypropane.
 5. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2-styryl-3-phenylbenzopyrylium perchlorate and 2-styryl-3-phenyl-4-methoxybenzopyrane.
 6. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2-phenylbenzopyrylium perchlorate and 2-phenyl-4-methoxybenzopyrane.
 7. The electrophotographic material of claim 1 wherein the sensitizer is the reaction product of 2-(p-methoxyphenyl)benzopyrylium perchlorate and 2-(p-methoxyphenyl)-4-methoxybenzopyrane. 